For the mashed potatoes: Add the potatoes and 1 tablespoon salt to a large saucepan and cover with water. Bring to a boil and cook over medium-high heat until fork-tender, about 15 minutes. Drain the potatoes and set aside to dry.
Whip together the cream cheese and butter in a large bowl with a hand mixer on medium speed until thoroughly blended, about 2 minutes. Add the still-warm potatoes alternating with the half-and-half. Whip until blended. Add in the pepper and garlic and season with salt to taste.
Grease a 9-by-14-inch glass baking dish with butter and pour the potato mixture into it. Bake right away, or cover and refrigerate for up to 2 days.
When ready to bake and serve, preheat the oven to 350 degrees F.
For the topping: Pour the melted butter over the potato mixture and bake until bubbly and slightly golden, about 45 minutes. Garnish with the chives and parsley. The potatoes can be kept warm in a 200-degree oven or tented with foil until ready to serve, up to 2 hours.